This invention relates to a method for controlling the operation of a burner and, more particularly, to controlling the fuel/air ratio of burners used to melt copper to avoid incorporating unwanted oxygen and/or hydrogen into the copper.
The melting of copper is a very important commercial process. As is well-known in the art and as discussed in U.S. Pat. No. 3,199,977 issued to A. J. Phillips et al. on Aug. 10, 1965, the disclosure of which is incorporated by reference, copper cathodes are the predominant form of copper produced industrially and the cathodes are generally flat rectangular shapes about one inch thick by about 25 inches to 40 inches, although larger or smaller sizes may be produced.
Although the cathodically deposited copper is commercially pure except for the usual impurities and unavoidable minor amounts of electrolyte (sulphates) physically present on the surface of the cathodes or occluded therein, the copper cathodes generally are not used per se because of their shape and physical properties, especially the grain structure of the deposited copper. To place them in more useful form, the cathodes must be melted and the molten metal cast into one or more semi-finished forms--for example, cakes, ingots, bars such as wire bars, billets and rods and similar shapes from which finished products are produced, such as for example, sheets, wire, tubes and the many other commercial products fabricated of commercially pure copper. However, it is important that the copper not become contaminated with commercially unacceptable amounts of oxygen and sulphur during the melting since from a commercial standpoint the melted . copper is essentially ruined and must be reprocessed through a series of steps to form a new cathode. This is a costly and time consuming procedure.
It is essential therefore, that the burners used to melt the copper not contaminate the copper with, for example, unwanted oxygen. In general, the fuel/oxygen (air) mixture is proportioned to contain insufficient oxygen to completely burn the fuel and the resulting melting flame is a reducing flame. For most industrial uses, the predetermined reducing conditions should be such that any oxygen incorporated into the copper is less than 0.05% by weight of the copper during the melting. Preferably, the predetermined reducing conditions are such that less than 0.035% and most preferably less than 0.01% by weight of oxygen are incorporated into the molten copper.
The burners described in Phillips et al. supra and U.S. Pat. No. 4,536,152 to Little and Thomas were specially designed to provide a high degree of fuel/air mixing to produce a uniform reducing flame to minimize unburned oxygen and possible copper contamination. The disclosure of U.S. Pat. No. 4,536,152 is hereby incorporated by reference.
While the prior art burners per se are important in the melting of copper, it is also very important to properly control the fuel/air mixture since an excess of fuel or air may produce a flame which will contaminate the copper and it is therefore an object of the present invention to provide a method for effectively melting copper and other metals and materials by controlling the fuel/air ratio of the burners used for the melting operation.
The predominant furnace for melting copper is the vertical shaft furnace using multiple burners as described in the Phillips et al. patent, supra., and the following description will be directed to this furnace for convenience.